One known shoe construction which is especially suitable for use in the manufacture of sports shoes involves injection moulding a liquid polyurethane material to form, on curing, a shoe sole on an upper carried by an appropriate footform. In carrying out this method the insole material used in shoe manufacture must be sufficiently impervious to the liquid urethane composition to prevent leakage of the urethane material to the inside of the shoe; in addition, the insole needs to be flexible but high in tensile strength both along and across the insole and low in extensibility both along and across the insole, i.e. having good dimensional stability, and, furthermore, as the shoe construction usually involves stitching the insole to the upper, the insole must be readily stitched.
The term "shoe" where used herein is intended to denote outer footwear generally whether ready to wear or in the course of manufacture, as the context permits.
One material which has been used for shoe insoles for sports shoes is made by needling a non-woven fibre fleece to a polypropylene scrim from one side of the scrim (that side which is intended to be adjacent the injected-on sole in the finished shoe); fibres of the non-woven fleece are needled through the scrim and the fibres needled through are coated (on the side of the material nearest to the scrim) by a suitable latex composition which, when dried, provides a coating on the insole of the shoe which has a sufficient degree of resistence to penetration by the liquid urethane composition used in manufacturing the sole. While this known material is reasonably satisfactory in use, it has some disadvantages. For example, in many instances the latex coating is not sufficiently impermeable, tending to lead to leakage of some soling composition to the inside of the shoe which is undesirable. Furthermore, some shoe manufacturers prefer to use the material with the impermeable side adjacent the soling compound--this can cause problems of adhesion of the soling material to the insole material and also lead to a coarser foam structure in the polyurethane soling material as the latex coating hinders dissipation of the gas generated during the urethane foaming process. In addition, needling of the non-woven fleece to the scrim considerably weakens the scrim reducing its tensile strength--although the latex coating recovers the tensile strength to some extent this weakening of the scrim is highly undesirable.